1. Field of the Invention
This invention relates generally to a method for cleaning the exterior surface of tubing located within the interior of a steam generator of the type ordinarily employed to produce large volumes of steam utilized to generate electricity. The invention more particularly relates to a method for removing the accumulation of ash from the exterior surfaces of the tubes and, still more particularly, to a method of using explosive detonating cord to produce controlled, sequential explosions whereby pressure waves and vibrations of the tubing are established to effect separation of the ash from the tubing.
2. Related Art and Problems Solved
Electric power generating plants commonly produce steam to operate turbines which in turn operate generators to produce electricity. The steam is produced by heating the external surfaces of tubing containing water wherein the tubing is housed in large structures referred to as steam generators. Commonly, the heat is provided by the combustion in the steam generator of gas, oil, coal, or other hydrocarbon fuels. Combustion of hydrocarbon fuels not only produces heat but also produces large amounts of solid waste material which is sometimes referred to herein as ash and sometimes as slag. Coal dust is a common hydrocarbon fuel source which contains numerous impurities that are not efficiently burned and also show up as solid waste material. Ash collects on the exterior surfaces of the tubing and acts as an insulative layer on the tubing.
It should be appreciated that this insulative layer reduces the overall efficiency of the steam generator by requiring additional combustion of fuel to properly heat the water within the tubes. In fact, when the tubing is properly cleaned, that is, when the insulative layer is removed, the thermal efficiency of the plant can be expected to increase by approximately 0.5% to 1%. When the enormous scale of a typical steam generator is considered, this relatively small percentage increase results in an extremely large dollar savings to the operating company.
Accordingly, it is known in the art to periodically clean a steam generator by a process featuring extensive washing of the ash with a high-pressure water solution; the process is commonly referred to as hydroblasting. Typically, hydroblasting involves such inherent problems as requiring a complete shut-down of the steam generator for as long as twenty days. Obviously, complete shut-down of the steam generator means that it cannot be doing what it is designed to do, produce steam to generate electricity.
During the period required to perform the hydroblasting, a crew of approximately sixteen people work twenty-four hours per day in relatively cramped and undesirable working conditions. The twenty-four hour per day requirement is a byproduct of using water as the cleaning agent. The combination of the water and ash can produce a cementitious like material, which, if allowed to dry, would also harden like cement and further exacerbate the clean-up. Accordingly, the ash removal work must proceed around the clock with prompt attention to removing the wet ash.
Moreover, while a steam generator typically includes provisions for removing dry ash that settles to the bottom of the generator, it is not equipped to handle wet ash. Therefore, a hydroblasting operation requires the use of expensive, wet-ash-handling equipment, as well as the extensive manpower required to operate it.
An additional byproduct of a hydroblasting operation is the production of sulfuric acid. The water combines with sulfuroxide in the ash to produce an acid that is highly corrosive to the tubing, as well as to any other metallic structure in the facility. Thus, careful attention must be given to the dilution or removal of the sulfuric acid to prevent undesirable corrosion and attendant repair of the facility.
The present invention is directed to overcoming one or more of the problems set forth above.